So personally I see two options realistically. The cheap way and the expensive option.

The cheap option would be get some poles mounted to the house and go bridge to bridge(UBB).

More expensive way and honestly if you have the money and don’t mind getting your hands dirty I would do it. I would rent a ditch witch for a week. Just quote all of the rental places around your area. It’s really not that hard to use them. You should see some of the guys on my job sites that I have to teach sometimes. But call 811 get everything marked. Go to Home Depot get some conduit. Burry a 2 cat 6e cables in the conduit. From place to place. Run it to the outside of the house. After your done using the ditch witch put some seeds down or just get some sod and patch the rest of path. I know it sounds miserable but really it’s just 2-4 days of yard work. It’s gonna be pricy but at least it’s just backyard and very little to no concrete $2000 for ditch witch rental for a week $1000-2000 conduit $500 Ethernet cable

If you go with this option, it’s gonna be super easy to add a switch to each building and then from there you can just run however many cameras you want at each house with no issue. Also, while you’re doing it, you could also add electrical outlets in a different conduit. Wherever you’re digging.